The veteran, who celebrates his 28th birthday on Thursday, won a battle of wills with top seed Jiri Novak of the Czech Republic, collecting a 6-7 (5-7), 6-4, 7-5 first-round victory at the Estoril Open.
Eight years ago, Van Lottum played his first professional match at the Estadio Nacional venue.
"This is really ironic," said the 105th-ranked player who lost two of three matches this season entering the tournament. "When I played here in a Satellite (event), Novak was the guy who won it."
The Dutchman went straight to his cell phone to tell his family how he claimed his first top 10 victory.
Van Lottum ended it on second match point, profiting from a final Novak error after the pair had traded breaks deep in the third.
"I was very tight at the end," Van Lottum said. "I'm just happy to have this win, we'll just see what happens."
Novak gained the top seed Sunday when Juan Carlos Ferrero of Spain pulled out before the draw with a lingering ankle injury. The Czech was devastated after now going without a clay title for more than 18 months.
"I was fighting, playing good tennis," Novak said. "But I didn't take my chances. I had so many chances to break in the second, but I couldn't make them. I lost concentration. It's tough to lose like this."
Robredo, twice a loser to the Italian veteran, secured a place in the second round with a 6-3, 6-1 win.
Argentina picked up two victories, with Jose Acasuso ousting Spain's David Sanchez, 6-3, 6-4, and Agustin Calleri routing 18-year-old Portuguese qualifier Diogo Rocha - playing in his first ATP event - 6-1, 6-0.
In women's play, French third seed Virginie Razzano beat German Barbara Rittner, 7-6 (7-5), 6-0; Croatian Silvja Talaja knocked out sixth-seeded Klara Koukalova of the Czech Republic 6-4, 6-4; and No. 8 Czech Iveta Benesova topped Tatiana Poutchek of Belarus, 6-3, 6-1.
Other unseeded winners were Jelena Kostanic of Croatia, Rossana Neffa De Los Rios of Paraguay and Stephanie Cohen Aloro of France.
Neffa De Los Rios advanced when her opponent Marta Marrero retired at 3-3 in the first set with a left ankle strain.
Cohen Aloro posted a 6-2, 6-3 win over young Russian Maria Kirilenko, the reigning U.S. Open Junior champion.
Kirilenko, who is allowed to play only 10 tournaments due to age restrictions, was helped into the tournament when men's star Yevgeny Kafelnikov asked for a wild card to be given to his compatriot.
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